Cast iron roll



Patented Aug. 9, 1932 PATENT OFFICE EMERSON K. LEWIS EUGENE WENZ, OFPITTSBURGH, PENNSYLVANIA CAST IRON ROLL No Drawing.

The invention relates to iron rolls, and especially to condensed graincast iron alloy rolls for use in rolling mills.

The metal rolling art has long sought an iron roll which possesses thecombination of ad quatestrength, satisfactory surface hardness andsuitable grain structure, and which possesses high enough interiorhardness to permit substantial dressing and grooving. Rolls as producedat resent are generally made from a high car 11 iron, and usuallycontain other hardening elements. The requisite surface hardness isobtained by suitably adjusting the composition, or by casting againstheavy chilling rings to obtain a hard, white iron outer chilled portion.However, whether cast against heavy chills, or against lighter chills toproduce the so-called condensedgrain rolls, the prior rolls havesuffered from the serious disadvantage that the interior, unchilledportion is considerably softer than the outer, chilled portion.Furthermore, and what is more serious, the inner zone becomesprogressively and rapidly softer toward the center.

As a result of the hardness differential between the outer and innerzones and within the inner zone/she rolls which have been producedheretofore have not been satisfactory because they must be discarded assoon as they are turned down through the hard outer portion. This isespecially true of grooved rolls used for rolling shapes or structuralforms. As soon as the roots of the grooves penetrate into the softerportion of a roll, it has to be discarded, because the inner, softerportions are not hard enough or sufficiently resistant to wear to permitfurther use.

An object of the invention is to provide a condensed grain cast ironroll having an outer condensed and an inner uncondensed portion, aclose-grained gray iron structure from surface to center, and having alow hardness differential from surface to center.

Another object is to provide a condensed Application filed March 29,1929. Serial No. 851,116.

grain roll of the type referred to in which the condensed portion mergesgradually into the uncondensed portion, and in which the hardness of theuncondensed portion is substantially uniform to the center.

A further object is to provide a condensed grain cast iron roll having aclose-grained gray iron structure from surface to center irrespective ofthe degree of chilling, and having high interior as well as surfacehardness.

Still another object is to provide a condensed grain cast iron rollrelatively low in carbon, having a close-grained gray iron structurefrom surface to center in which the condensed outer portion mergesgradually into the inner uncondensed portion, and in which the hardnessof the interior portion is substantially uniform to the center.

Other objects are to provide a condensed grain cast iron roll having aclose-grained gray iron structure from surface to center irrespective ofthe degree of chilling, which is low in carbon and contains substantialamounts of chromium and nickel, and which is especially adapted for usein rolling shapes.

In'accordance with the invention the rolls 4,

are made from a cast iron alloy containing relatively low amounts ofcarbon together.

'wi h substantial amounts of nickel, chromium, and silicon, by castingthe iron alloy to form outer condensed and inner uncondensed portions.Preferably, they are cast against the light chills used in makingcondensed grain rolls. The rolls thus formed have a close-grained grayiron structure from surface to center, and the condensed portions merge.gradually into the uncondensed portions. A particular characteristic ofthese rolls is that the hardness and graphitic carbon content of theuncondensed portion is substantially uniform u to the center; also theypossess a very'low hardness and graphitic carbon differential fromsurface to center. Although the invention preferably embodies condensedgrain rolls, it is a characteristic of the cast iron alloys used in thepractice of the invention that, even 5 when cast in very heavy chillsthe rolls still possess a gray iron structure from surface to center,thecharacteristics of which are likely those numerated above.

The iron alloy used in the invention is characterized by a low carboncontent relative to that commonly used in cast irons, and it contains asomewhat higher amount of chromium than is usual in acast iron used forrolls, together with substantial amounts of softening elements such assilicon, and hardening elements such as man- .ganese and nickel, as wellas other metals and metalloids, for example, sulfur and phosphorus. Inthese alloys the carbon may vary from about 2.0 to 3.4 per cent, the higher ranges within these limits being preferred for most purposes.Silicon, which exerts its well known effects, ranges from about 1.25 to3.0 per cent; This element will be varied in the well understood manner,in accordvance with the characteristics desired in the roll, its size,degree of chill, and the like. In general, from about 0.4 to 1.0 percent of manganese may be used. Chromium, which 8 is used for itshardeningveffect to compensate for the reduction in carbon, may range.

from about 0.80 to 2.5 per cent, and preferably from about 1.3 to 2.5per cent. The nickel content of the alloys may be varied within ratherwide limits, from about 0.4 to 3.0 per cent. Manganese and chromium tendto prevent the formation of graphitic carbon, and may for this reason hetermed carbon-retaining elements. The alloys may phorus. This element,however, is not always easy to control in cast irons, and smallvariations are permissible. The sulfur is kept low, but for best resultsis present in an amount greater than about 0.03 per cent.

Rolls thus made in accordance with the invention have a gray ironstructure throughout, which is close and fine-grained entirely to thecenter, and which possesses character- .istics novel in such rolls whichmake them superior for certain purposes to prior rolls. The condensedportion of the rolls merges gradually into the uncondensed portion, and

there is no distinct line of demarcation be- 7 tween them. As a matterof fact, it is difiicult to determine by visual examination of afractured or cut groove surface, where the chilled portion ends. Thisstructure is of advantage, because it eliminates sudden changes inphysical properties. The graphitic carbon is present in finely dividedform, and the grain texture is distinctly that of condensed grain rolls.There is this difference as comparedwith prior rolls: In thoseheretofore made, the graphitic carbon content increases contain about0.04 to 0.09 per cent of phos-- quite sharply in passing inwardly fromthe surface into the chilled zone, with the resuit that the rolls aremuch softer and weaker at the juncture of that zone with the inner,unchilled zone. Furthermore,- going inwardly toward the center throughthe unchilled zone, the graphitic carbon increases gradually,and-generally as the center is approached the structure becomes mottledand porous because of the high amount of graphitic carbon. Thus theinner portions of the prior rolls become progressively softer andweaker. These characteristics are decidedly disadvantageous, chieflybecause the amount the roll could be turned down (and consequently itsuseful life) is limited to the depth of the outer, chilled portion.Espeoially is this a disadvantage in the case of grooved rolls.

In the rolls provided according to this invention the graphitic carbonincreases somewhat, but to an appreciably lesser extent than in priorrolls, in passing from the surface to the end of the condensed portion;and what is especially important, the graphitic carbon content from theend of the condensed portion to the center of the roll is uniform, orsubstantially uniform. Owing to the composition of the rolls and theircasting behavior, the surface hardness is high, and this combined withthe texture of the grain makes these rolls suitable for roughing orintermediate rolling. The hardness, in consequence of the foregoingproperties, does not decrease as much as in prior rolls in passinginwardly toward the center, there being a relativelv low hardnessdifferential between the surface and the end of the condensed zone, andthe hardness of the uncondensed portion is relatively uniform up to thecenter. The rolls according to the invention are thus admirably adaptedfor rolling shapes and structural forms, because the interior of theroll is hard enough and of sufliciently uniform hardness to permitcutting the grooves or tongues well into the roll.

While the preferred practice of the invention is to form condensed grainrolls, they may be cast against the massive chilling rings used to makechilled rolls. In such cases also the rolls possess a gray ironstructure throughout, which is similar in appearance and properties tothat described hereinabove, the properties being modified in the mannerto be expected from severe chilling. Thus it will be understood that theproperty of securing a roll having condensed and uncondensed portions ofgray iron merging one into the other and in which there is a lowhardness differential from surface to center and particularly in theuncondensed zone, is a characteristic of the invention irrespective ofthe degree of chilling.

In general it may be said that where great toughness is desired, forrolls subject to severe shock, the lower ranges of composition givenwill be used. Rolls made from the higher ranges are in general lesstough, but of greaterhardness, and possess high wear resistance.Properties intermediate these may be secured by suitable selection ofthealloy components.

The following actual example illustrates the important advantages of theinvention. A cast iron alloy selected to give medium hardness with adesirable combination of toughness and strength and containing about3.17 per cent of carbon, 1.75 per cent of silicon, 0.57 per cent ofmanganese, 1.35 per cent of chromium, 0.52 per cent of nickel, 0.038 percent of sulfur, and 0.097 per cent of phosphorus was cast in the form ofa roll having a body 22% inches in diameter and 27 inches long, withnecks 13 inches in diameter and 14. inches long. The roll was castagainst light chilling rings to give the condensed grain structure. Atransverse slice 1 inches wide was out from the center of the roll body,and holes inches in diameter were drilled 1 inch apart from center tocenter across a diameter of this section, the turnings from each holebeing segregated for analyst. Scleroscope hardness tests were also madeon this section, along a diameter thereof. The results are shown in thefollowing table, each figure being the average of correspondingdiametrically opposed points:

Distance Graphitlc from Scleroscope surface carbon Inches Per centHardness 46. 1 1 1. 71 44. 2 2 1. 86 42. 6 3 1. 01 41. 4 4 1. 97 40. 15 1. 86 40. 3 6 1. 94 39. 6 7 1. 96 39. 5 8 1. 99 38. 6 9 1. 99 38. 610 1. 94 3B. 2

These data show that, within the limits of experimental error, thegraphitic carbon content and the hardness remain substantially constantfrom a point about three inches from the surfaceup to the center, andthat from the surface, or close to the surface, to the center, there isbut a lowgraphitic carbon and hardness differential, i. e., the innerand outer zones approximate each other in hardnests. They show furtherthat in this roll the difierence in hardness between the outer condensedportion and the inner uncondensed portion is only 8 points, which is solow that rolls accordingto the invention can. be cut down to an extentwhich has heretofore been impossible.

Tensile and transverse test bars were cut from theperiphery of the rollbody, the average tensile strength being 27250 pounds per square inch,and the average of the transverse or bending tests being 3942 pounds persquare inch, the supports in these tests being spaced 10% inches apart.Tensile test bars were cut from the transverse body section used for thehardness tests and carbon analyses. These showed strengths of about25000 pounds per square inch at 3 inches from the surface, and fromthere inwardly to the center the strength averaged about 20000 poundsper square inch.

As further showing the properties independent of the degree of chilling,the drag neck, which was of course cast sand, was sectioned 6% inchesfrom the body, and turnings for analysis taken as before, which showedthe graphitic carbon content to be substantially constant from a pointabout 1 inch from the surface to the center. The data are given inthe'following table:

233 Graphitic f carbon i. ace

I aches Per cent Surface 1. 79

6 1. 93 Center 1. i

As further illustrative of the benefits of the invention, the followingdata obtained from another roll cast and tested as in the precedingexample are cited. The body of this roll was 42 inches in length and 30%inches in diameter, and the necks were 19 inches long and 18 inches indiameter. The average analysis of drillings taken across the to be' bodyas in the case of the preceding roll was as follows:

- Per cent Total carbon 2.80 Combined carbon ",1 1.15 Manganese 0.33Chromium 1.13 Nickel ....s..-. 1.60 Silicon -Q Sulfur 0.037 Phosphorus0.065

- pounds per square inch three inches below the surface, and from thereinwardly to the center the average strength was 25430 pounds per squareinch.

Hardness tests and graphite carbon analyses were made along a diameterof a slice taken from the body, as in the preceding example, the resultsbeing as follows:

Dlsgnce from 65221331211510 3 c1 eroscope Inches Per cent Hard-ness )458. 9 56 55. 1 1 1. 41 53. 9 2 1. 69 51. 2 3 1. 67 48. 1 4 1. 65 46. 35 1. 71 45. 1 6 1. 70 43. 7 7 1. 67 42. 8 1. 72 41. 9 1. 67 43. 4 10 1.66 41. 0 11 1. 68 39. 4 12 1. 64 39. 1 l3 1. 60 38. 1 14 1. 61 37. 7 15%(Center) 1. 69 36.6

As in the case of the first-cited roll, the graphitic carbon ispractically constant from the end of the condensed outer portion to thecenter of the roll. In this case the condensed portion extended aboutfour inches into the roll. Likewise, the hardness differential from thebeginning of the uncondensed portion to the center is very low. And allof the advantages previously discussed were present in both rolls.

Anal sis of the rolls made across a diameter of the ody and of the neckshow, in addition'to the foregoing characteristics, that there issubstantially no tendency toward segregation of any of the elements,even in very large rolls. This is, of course, of great advantage.

The invention provides condensed grain rolls whlch from all standpointsovercome the disadvantages of prior rolls. These rolls possess condensedand uncondensed portions which merge gradually lnto one another,

' which approximate one another in hardness,

and which are of afinegra-inthroughout. The interior uncondensedportions possess a uniformity of hardness hitherto unobtainable, andthese properties make the normal life of the rolls very great, becausenot only is their strength sufiiciently high, but they may be turneddown or grooves cut deeper into the uncondensed portions than waspreviously possible, with fully adequate strength, interior hardness andresistance to wear.

According to the provisions of the patent statutes, we have explainedthe principle and mode of operation of our invention, and have describedwhat we now consider to represent its best embodiment. However, wedesire to have it understood that, within the scope of the appendedclaims the invention may be practiced otherwise than as specificallydescribed.

We claim as our invention 1. 'As a new article of manufacture, acondensed grain cast iron roll formed of an iron alloy containing about2 to 3.4 per cent of carbon, about 0.8 to 2.5 per cent of chromium about0.4 to 3.0 per cent of nickel, about 1.25 to 3.0 per cent of silicon,and about 0.4 to 1.0 percent of manganese, proportioned to provide aclose grained gray iron structure from surface to center irrespective ofthe degree of chilling, and having outer condensed grain and inneruncondensed portions, a low hardness differential from surface tocenter, and substantially uniform hardness in said uncondensed portion.

2. As a new article of manufacture, a condensed grain cast iron rollformed of an iron alloy containing about 2 to 3.4 er cent of carbon,about 1.3 to 2.5 per cent 0 chromium, about 2.5 per cent of silicon,about 0.4 to 3 per cent of nickel, and about 0.4 to 1 per cent ofmanganese, proportioned to provide a close grained gray iron structurefrom surface to center irrespective of the degree of chilling, andhaving outer condensed grain and inner uncondensed portions, a lowhardness differential from surface to center, and substantially uniformhardness in said uncondensed portion.

In testimony whereof, we hereunto sign our names.

EMERSON K. LEWIS. EUGENE WENZ.

